Electric circuit for incandescent lamps



P 1952 M. R. DOUGLASS ELECTRIC cmcun FOR' INCANDESCENT LAMPS Filed June 29, 1950 4 IN VEN TOR. flyzyfiozglass BY HIS 41 7mm Patented Apr. 29, 1952 ELECTRIC CIRCUIT FOR INCAN- DESCENT LAMPS .Myrl R- Douglass, .Edgewood, Pa., assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania Application June 29, 1950, Serial No. 171,215

3 Claims. (01. 315-186) My invention relates to an electric circuit for incandescentlamps, and particularly to a circuit which is effective to prevent ahigh current surge when a lamp which has previously been extinguished is connected in series with another lamp already burning, across a voltage sufficient to energize both lamps.

,It is customary in railway signaling to employ incandescent lamps as light sources for signals and .in certain applications use is made of signals having at least two lamps which may be controlled so as to provide a first aspect when one of the lamps is li hted and a second aspect when both of the lamps are lighted. In such cases it is essential that. the control of the lamps be such that if both lamps are to be lighted to display the second aspect the extinguishment of either lamp will cause the other lamp to be extinguished also, and in this manner avoid having one signal lamp lighted to display .its aspect falsely when both. lamps should be lighted. In, these cases, therefore, it is sometimes necessary to shift from one aspect where one lamp is lighted to another aspect by lighting the other lamp while retaining the one lamp lighted, and to protect against the display of an improper aspect if either of the lamps is burned out the two lamps are connected in series when both arerequired to be lighted so that the failure of either lamp will cause the other tobe extinguished also. In connection with such signals appropriate voltage sources are of course provided for energizing the two lamps of the signal with. a voltage divider arrangement being used .to supply only the rated voltage to the one lamp when the other is dark, and the rated voltage to each of the two lamps when they .are connected .in series.

- An incandescent lamp has the characteristic that when the filament of the lamp reaches its operating resistance the filament is incandescent and remains incandescent by dissipating in the form of. light and heat the power that is consumed in the lamp. The. limited ability of the lamp tov dissipate heat results in the melting of the filamentfif any substantial increase in power is applied to the lamp over and above that required to maintain the filament at incandescence. However, a lamp filament which reaches its operating resistance at incandescence is of relatively low resistance when the filament is coldrandif a filament in the incandescent conchtion is shifted from its rated voltage source to a series connection with a cold -filament across a source having a voltage suffi'cient effectively to energize both lamp filaments at incandescence,

Y substantially all of the voltage. drop will appear momentarily across the one filament that is already in its incandescent condition and then the voltage across that filament will decrease to its rated voltage as the second filament becomes heated up and reaches incandescence. The power (1 R) required to be dissipated under these conditions by the one filament in its incandescent condition may, and often does, pass the limits of effective dissipation with the result that such filament either melts immediately or becomes seriously damaged.

A prime object of my invention is to provide a novel and improved circuit of the type described which is effective to prevent a high current surge through the, filament of a lamp which is already burning when another lamp previously extinguished is connected inseries with'it.

To attain the object of my invention I provide a slow pick up relay having a make-beforebreak contact to complete the series connection, which relay is efiective to first connect the lamps across separate portions only, of the total voltage required for the series connection, so that the cold filament may reach its rated resistance before the series connection is completed.

I shall describe one form of apparatu embodying my invention and shall then point out the novel features thereof in claims.

Referring to the drawing, two incandescent lamps, respectively designated by the reference characters R. and Y, and which may be two lamps of a railway light signal, are shown associated with a source of electrical energy effective to energize both lamps at the rated voltage when the lamps are connected in series. The voltage source as shown in the drawing is'the secondary winding S of a transformer '1 having its primary winding P connected to a suitable source of alternating current conventionally represented by the reference characters BX and CX, but it is understood, of course, that other suitable sources of electrical current may be emp oyed f r ener izin the two lamps Rand Y'- A suitable continuity transfer or make-beforebreak contact mechanism which may be operated in any suitable manner is provided for selectively connecting either lamp R across a portion of winding S or both lamps R and Y in series across the full secondary winding S. The contact mechanism comprises a movable contact member I of suitable continuity transfer type which may, for example, be provided with a bifurcated end portion formed on or attached to the free end of member ,I, and two fixed contact point .2 and-.

The member I is operable between two extreme positions in which its bifurcated end portion respectively engages one or the other of the two fixed points 2 and 3. The bifurcated portion of member I is proportioned and arranged in such a manner that in the travel of member I between either one of its two extreme positions to the other the one leg of the bifurcation will remain in engagement with the one fixed contact member until after the other leg of the bifurcation makes contact with the other fixed contact. That is, when member I operates from contact point 2 to point 3, for example, member I makes contact through its one bifurcated leg with fixed point 3 before the other bifurcated leg of member I breaks engagement with fixed point 2. The movable contact member I may be operated manually, pneumatically or by any other suitable means and as shown is operated by the armature of an electromagnetic relay. In any event the operation of the movable member I should be such that the period of overlap when the two bifurcated legs of member I are in contact with the two fixed points 2 and 3, respectively, should be not less than approximately one-sixth of a second.

Secondary winding S has two end terminals designated respectively by the reference characters B and N and a tapped mid point designated by'the reference character C. One end terminal B of winding S is connected through the filament of lamp R to the heel of movable contact member I, while the other end terminal N of winding Sis connected through the filament of lamp Y to fixed contact point 3. The mid terminal tap C of winding S is connected to the other fixed point 2 so that when member I is in its one extreme position as shown in engagement with fixed point 2 the filament of lamp R is connected across the portion BC of winding S, and the parts are so proportioned that in this condition winding portion BC supplies rated voltage to lamp R to cause the filament of that lamp to be heated to incandescence. If, now, member I is operated to its other extreme position, the two bifurcated legs of member I in the mid stroke position of that member bridge the two fixed contact points 2 and 3 and close a circuit from terminal N through the filament of lamp Y, fixed point 3, the bifurcated legs of member I and fixed point 2 to themid tap terminal C of winding S while maintaining the filament of lamp R connected across the first portion BC of winding S. The parts of the circuit traced for lamp Y are also so proportioned that in this condition rated voltage is supplied to lamp Y from the portion C-N of winding S. The bridging connection between fixed points 2 and-3 established by the bifurcated legs of member I is maintained, as pointed out hereinbefore, for approximately one-sixth of a second or long enough for the filament of lamp Y to become heated and build up a substantial resistance due to current supplied from the lower portion C-N of winding S before the bifurcated leg of member I breaks engagement with fixed point 2, at which time the filaments of the two lamps R and Y are connected in series across the two end terminals B and N of winding S, through a circuit which passes from terminal B through the filament of lamp R, movable contact member I, fixed contact point 3 and the filament of lamp Y to the other terminal N of winding S.

When contact member I is operated from its other extreme position to its one extreme position, the two lamps R and Yare first shifted from their connection in series across the terminals B and N to a connection in the mid stroke position of member I where the two bifurcated legs bridge fixed points 2 and 3 and in which the lamp R is connected across terminals B and C and lamp Y is connected across terminals C and N. Then when contact member I reaches its one extreme position the connection of lamp Y with its terminals C and N is opened and lamp R is maintained energized at its rated voltage supplied from terminals B and C.

It follows that I have provided a circuit arrangement capable of shifting a lamp filament in its incandescent condition from its rated voltage source to a circuit which includes that lamp filament and a previously unlighted lamp filament and which circuit is supplied with voltage effective to energize both filaments at incandescence. This shift I obtain by using a single movable contact member operable from one extreme position in which one lamp filament is connected across an appropriate voltage, through an intermediate position in which the one lighted filament is maintained connected across its source while the second filament is momentarily connected across another voltage source so as to become preliminarily heated, to another extreme position in which the two lamp filaments are connected in series circuit across the two voltage sources also connected in series; the arrangement being such that the preliminary heating of the second filament will build up its resistance to a value such as to prevent damage to the one filament that is in its incandescent condition when the two lamp filaments are connected in series with the full voltage source.

Although I have herein shown and described only one form of electric circuit for incandescent lamps embodying my invention, it is to be under stood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In an electrical circuit, a source of voltage, a first lamp, a first circuit including a normally closed relay contact connecting said first lamp across a portion of said source, a second lamp, a relay effective when energized for connecting said second lamp across another portion of said source through said relay contact and effective when picked up to open said normally closed relay contact and thereby effectively connect both said first and second lamps in series across said source.

2. In combination with two incandescent lamps, a source of current having two end terminals and a mid-terminal, said source being effective to energize the filament of either lamp to incandescence when the lamp is connected across an end terminal and said mid-terminal and the filaments of both lamps to incandescence when the two lamps are connected in series across the two end terminals, a continuity transfercontact operable between two extreme positions in which it respectively engages one or the other of two fixed contact points and effective in mid-stroke position to bridge the two fixed contact points, a circuit connection between one of said fixed contact points and said mid-terminal, a circuit connecting the filament of one of said lamps between one end terminal and said continuity transfer contact, and a circuit connecting the filament of the other of said lamps between the other end terminal and said other fixed contact points.

3. In combination with two incandescent lamps, a source of current effective to energize the two lamps at their rated voltages when the lamps are connected in series across said source, a continuity transfer contact operable between two extreme positions in which it respectively engages one or the other of two fixed contact points and efiective in mid-stroke position to bridge the two fixed contact points, means for operating said continuity transfer contact between its said two extreme positions, a circuit completed in one extreme position of said continuity transfer contact for supplying one of voltage from a first portion of said source, a

said lamp filaments with current-at the rated plied with current from said first portion of said source, and a circuit completed in the other extreme position of said continuity transfer contact for connecting both of said lamps in series across said source.

MYRL R. DOUGLASS.

No references cited. 

